Coast FIRE by Age

The Coast FIRE calculation discounts a future retirement target back over the number of years remaining until the selected retirement age.

The relationship is:

Current age affects:

For example:

The future retirement target can remain unchanged.

Only the amount of time available for modeled growth changed.

Related: Coast FIRE Formula Explained

To isolate the effect of age, keep every other input unchanged.

Use:

Now change only the current age.

Every row uses the same:

• retirement age;
• retirement spending;
• withdrawal-rate assumption;
• future retirement target;
• return assumption;
• inflation assumption;
• and fee assumption.

Only current age changes.

The table therefore shows the effect of changing the remaining compounding period rather than changing the retirement goal.

See the exact methodology: Coast FIRE Calculator Assumptions & Methodology

In the example above, the modeled Coast FIRE target at age 25 is approximately:

That result assumes:

until the selected retirement age of 65.

It is not a universal Coast FIRE number for every 25-year-old.

Changing retirement spending, retirement age, return, inflation, fees, or the withdrawal-rate assumption changes the result.

Using the same example assumptions, the modeled Coast FIRE target at age 30 is approximately:

The model has:

until age 65.

A real user question such as “How much should I have for Coast FIRE at 30?” therefore cannot be answered by age alone.

The calculation also needs a future retirement target and growth assumptions.

The $340,403 figure is an example model output, not an age-30 savings benchmark.

Using the same assumptions, the modeled Coast FIRE target at age 35 is approximately:

There are:

until the selected retirement age of 65.

Compared with age 30, the retirement target remains $1.25 million.

The modeled growth period is five years shorter.

That shorter period is what changes the current Coast FIRE target in this example.

Using the same assumptions, the modeled Coast FIRE target at age 40 is approximately:

The remaining growth period is:

until age 65.

This does not mean every 40-year-old needs $493,626.

It means $493,626 is the amount produced by this specific set of model inputs.

A different retirement target or a different growth assumption would produce another result.

Using the same assumptions, the modeled Coast FIRE target at age 45 is approximately:

There are:

until the selected retirement age.

The retirement target is still:

The Coast FIRE number is larger than the age-40 result because the model has five fewer years for the current amount to compound toward that same future target.

Using the same assumptions, the modeled Coast FIRE target at age 50 is approximately:

The modeled growth period is:

until age 65.

Again, this is not a recommended retirement balance for age 50.

It is one mathematical scenario using the same retirement target and assumptions as every other row.

Investor.gov explains compound growth as earning a return on invested money and then earning returns on those accumulated returns over time.

Its Compound Interest Calculator separately asks for:

• initial investment;
• monthly contribution;
• length of time;
• estimated interest rate;
• and compounding frequency.

For the basic Coast FIRE target, the central age relationship is the length of time.

If the future target remains fixed, reducing the number of years available for growth means a larger starting amount is required under the same growth assumption.

That is a mathematical relationship.

It is not a judgment about whether one age is better than another.

Current age changes the amount of time remaining to reach the future target.

The future retirement target in this site's basic framework is primarily produced from:

and

For example:

with:

produces:

Changing current age from 30 to 40 does not automatically change that $1.25 million target.

It changes how many years remain to grow toward it.

At age 40, the calculation simply has a shorter growth period than the same scenario at age 30.

In the consistent example:

Whether a particular current investment balance is below, at, or above the age-40 target is a separate calculation.

The formula itself does not classify age 40 as early, late, good, or bad.

In the example:

leaves:

until the selected retirement age of 65.

That produces a modeled Coast FIRE target of:

under the selected assumptions.

Another person at age 50 could have a different target because the retirement spending, selected retirement age, withdrawal-rate assumption, or growth assumptions are different.

Age alone does not determine Coast FIRE status.

The formula does not define a minimum Coast FIRE age.

A younger current age produces a longer modeled growth horizon when the selected retirement age stays unchanged.

For example:

The calculation can be performed at either age.

Whether assumptions about spending, retirement age, and investment growth remain useful decades later is a separate question from whether the arithmetic can be performed.

Investment targets and projections are hypothetical.

The U.S. Securities and Exchange Commission states that targets and projections do not represent actual future performance and that past performance cannot predict future performance.

Two people can both be 30 and use completely different:

• retirement ages;
• retirement spending;
• withdrawal-rate assumptions;
• return assumptions;
• inflation assumptions;
• investment fees;
• pension assumptions;
• or other modeled retirement income.

For example, one person might model retirement at:

while another models retirement at:

Even with the same future retirement target, the second scenario has ten fewer years for modeled compound growth.

The Coast FIRE targets therefore do not have to match.

A Coast FIRE number such as:

and another Coast FIRE number such as:

can both be mathematically consistent if they use different retirement targets, retirement ages, or growth assumptions.

The useful comparison is not only:

“What age are they?”

It is:

“What retirement target, retirement age, and assumptions produced their number?”

This is why an age table should be read as a controlled mathematical example rather than a universal benchmark.

The Coast FIRE target changes because the endpoint of the growth period changes.

Suppose the current age stays:

Retirement at:

provides:

of modeled growth.

Retirement at:

provides:

Those are different Coast FIRE scenarios.

Current age stayed the same.

The selected retirement age changed.

That distinction is important when comparing age-specific Coast FIRE numbers.

The age 65 used in this guide is a selected Coast FIRE retirement-age assumption.

It is not being presented as a Social Security rule.

The Social Security Administration states that full retirement age is 67 for people born in 1960 or later.

SSA also permits retirement benefits to begin at other eligible ages under its rules, with benefit amounts affected by claiming age.

Those Social Security rules are separate from the retirement-age input selected in a Coast FIRE calculator.

The calculator can model retirement at 65 without claiming that 65 is the reader's Social Security full retirement age.

Current age and modeled investment return are separate inputs.

Changing:

to:

does not automatically change:

or the resulting modeled real-growth assumption.

If the return assumption changes too, that is a second model change.

To understand the effect of age alone, the return assumptions should remain unchanged across the comparison.

Related: How Return Assumptions Change Coast FIRE

The Coast FIRE target asks how much would need to be invested at the current age for modeled growth alone to reach the future retirement target.

Future contributions can be modeled as a separate portfolio path.

For example:

Age:

Modeled Coast target:

A scenario with:

and another scenario with:

can have different projected portfolio balances.

The underlying Coast FIRE target can remain $409,917 if retirement age, spending, return, inflation, fees, and withdrawal-rate assumptions remain unchanged.

The values in this guide answer a narrower question:

What amount does the Coast FIRE formula produce at each current age when every other selected input is held constant?

They do not establish:

• what someone should have saved;
• whether someone is ahead or behind;
• whether retirement is funded;
• whether someone can stop contributing;
• or whether the assumptions will occur.

That is why the page uses:

rather than: